Abstract
In vascular smooth muscle, it has been described that testosterone (TES) produces relaxation by blocking L-type Ca2+ channels. Recently, we found that L-type Ca2+ and store-operated Ca2+ (SOC) channels are the main membranal structures that provide extracellular Ca2+ for carbachol (CCh)-induced contraction in airway smooth muscle (ASM). We studied the possible interactions between L-type and SOC channels in TES-induced relaxation in guinea pig ASM. TES (10, 32, 100, and 178 mu M) induced a complete relaxation of CCh-precontracted tracheal smooth muscle, and indomethacin partially inhibited this response. In single myocytes, the KCl-induced intracellular Ca2+ increase ([Ca2+](i)) was decreased by 32 and completely blocked by 100 nM TES. This androgen (32 and 100 mu M) significantly diminished (similar to 25 and 49 %, respectively) the capacitative Ca2+ entry. Myocytes stimulated with CCh produced a transient Ca2+ peak followed by a sustained plateau. D-600 was added during the plateau phase, and a partial diminution (similar to 35 %) was observed. A greater decrease (similar to 78 %) was seen when 2-aminoethyl diphenylborinate (2-APB, SOC antagonist) was used. The combination of both drugs completely abolished the Ca2+ plateau induced by CCh. TES (100 mu M) also completely abolished the CCh-induced Ca2+ plateau. Indomethacin significantly diminished this effect of TES. PGE(2) and butaprost proportionally decreased the Ca2+ plateau as indomethacin blocked it. Sarcoplasmic reticulum refilling was partially, dependently, and significantly diminished by TES. We concluded that TES-induced relaxation involves blockade of L-type Ca2+ channels at nanomolar and SOC channels at micromolar concentration and PGE(2) seems to be also involved in this phenomenon.